High-precision studies in fundamental physics with

slow neutrons

Oliver Zimmer

Institut Laue Langevin

ILL, 20 September 2016

Topics

• The impossible particle and its properties

• Search for an electric dipole moment of the neutron

• Short-range gravity

• Test of Einstein’s E = mc2

The neutron before Chadwick

The neutron before Chadwick

“Such an atom would posses striking properties. Its outer field would vanish [...] and therefore it should easily penetrate matter. The existence of such an atom is presumably difficult to observe with a spectrograph, and ...“

(„Nuclear Constitution of Atoms“, Proc. Royal Soc. 1920)

The neutron before Chadwick

“Such an atom would posses striking properties. Its outer field would vanish [...] and therefore it should easily penetrate matter. The existence of such an atom is presumably difficult to observe with a spectrograph, and it could not be stored in a closed vessel.“

(„Nuclear Constitution of Atoms“, Proc. Royal Soc. 1920)

How to store it nevertheless?

Mirror reflection under any angle of incidence

UCN can be trapped in “neutron bottles”

Trapping potential #1:

neutron optical potential V + iW

Physical origin:

• neutron scattering by nuclei

• interference of incident and scattered waves

• refractive index:

Typical values for V:

Be: 252 neV, Al: 54 neV, Ti: -49 neV

Trapping potential #2:

neutron gravity mgz

as good for trapping (if bottle is tall enough):

for z = 1 m: E = 100 neV

Trapping potential #2:

neutron gravity mgz for z = 1 m: E = 100 neV

Trapping potential #3:

magnetic interaction ±µB

for B = 1 T: E = ±60 neV

Adiabatic spin transport if

Magnetic gradient fields suppress losses due to wall collisions

mT fields sufficient in typical situations

Neutron properties:

nEDM

neutronlifetime

???

nuclear few-bodyinteractions

Heavy elements

n-gravity

nn oscillations

+

-

magnetic

momentE

DM

Search for an electric dipole moment of the neutron

+

-

Violation of fundamental symmetries

+

-

+

-

+

-

T

P

• A non-zero particle EDM violates T (time reversal symmetry) and parity P

• If we assume CPTconservation, also CP is violated, which is needed to explain the matter/antimatter asymmetry in the Universe

Purcell and Ramsey, PR 78 (1950) 807

• CP violation within the Standard Model (SM) is too weak to explain the matter/antimatter asymmetry in the Universe

• nEDM tiny in the SM (10-31 ecm), but large in many beyond-SM theories

• nEDM sensitive probe to search new fundamental forcesPendlebury and Hinds, NIM A 440 (2000) 471

RAL/SUSSEX/ILL experiment:

B0

Ultra-cold neutrons (UCN)

trapped at 300 K in vacuum

~ 0.5 m

How is it measured?

po

lari

zati

on

1 - L („detuning“)

n 2d

ET N

EdBL nn~

EDM changes frequency:

Particle beam or trapped particles(...spin echo)

E

Ramsey’s method

Experimental sensitivity:

0 5 10 15 20

29.9260

29.9265

29.9270

29.9275

29.9280

29.9285

29.9290

29.9295

10-10

T

Ne

utr

on

re

so

na

nt

fre

qu

en

cy (

Hz)

Run duration (hours)

7.7882

7.7884

7.7886

7.7888

7.7890

rati

o o

f p

rece

ssio

n f

req

ue

nci

es

199Hg co-magnetometer for correction of magnetic field drifts

|dn| < 2.9 10-26 e cm (90% CL)

Best result so far (RAL / Sussex / ILL)

• 10-22 eV spin-dependent interaction

• one spin precession per half year

C.A. Baker et al., PRL 63 (2006) 131801

Next steps?

• World-wide effort: projects at PSI, SNS, TRIUMF, TUM, PNPI, ILL

• Accuracy goal: below 10-27 ecm

• needs new UCN sources, excellent magnetic shielding…

n

n

r

L

r

mmg

r

mmGF

2

21

2

21

Modification of gravity with n additional dimensions at distances r < R:

Short-range gravitySmall extra-dimensions:Explanation why gravity is such a weak force?

New spectroscopic tool:

First observations (2002)

V. Nesvizhevsky et al., Nature 415 (2002) 299

Rabi-type spectroscopy of gravityqBounce collaboration (H. Abele, T. Jenke…)

Most recent results on Gravity Resonance Spectroscopy

Ramsey spectrometer for gravity statesH. Abele et al., Phys. Rev. D 81 (2010) 065019

Advantages:

• Long flight path smaller uncertainty E

• static central mirror for free state evolution

Snapshots of II2 with 1.5 m resolution

E = mc2

• need process, where mass is converted in energy

• thermal-neutron capture reaction:

i

i

LL γ X n X 11

thermal energies

~10-2 eV

excess energy:

several 106 eV

total energy uncertainty: < 10-8

How can we test it?

i

L

i

LL

c

hNAAA

X)(

110 X)(X)(n)(

1

A31

X)( 1 LA

i jK

j

L

i

KL

c

hNAA

Y)(

1

X)(

110 Y)(X)(

11

A311

Penning trap measurements (4 masses)

Gamma-ray wavelength measurements

(2 nuclides after neutron capture)

molar Planck constant

? )γ( X)](X)(n)([ 21

i

i

LL Ecmmm

In terms of mass units A relative to an atomic mass scale u = 10-3/NA kg :

hchE )γ(

m

qB Double crystal monochromator

GAMS

Which isotopes?

Pe

Penning Trap: A(L,L+1X) can be measured with 10-11 relative uncertainty!

Need mass values for two pairs of stable isotopes

= 0.3 barn

= 0.17 barn = 0.55 barn = 43.7 barn

Atomic Mass data

available

What is needed to determine gamma energies (or wavelengths) with high accuracy?

A 10-11 relative uncertainty on A requires measurements with accuracy 10-8

is necessary but insufficient

High accuracy use gamma spectroscopy based on Laue diffraction

Bragg’s law for photons

sin2dE

hcn

222

~

d

d

E

E

d/d < 10-8

Need absolute measurements of:

• lattice constant d

• scattering angle

Flat double-crystal monochromator spectrometer

for gamma rays: GAMS

measures instrument response

contains additional broadening

dispersive non-dispersive

sin2dE

hcn

Implantation of spectrometer

Neutron Flux: 5×1014

Targets: 0.1 – 10g

Target change during reactor cycle

Flat Crystals:

• Resolution: 10-6

• Eff. Solid Angle: 10-11

• absolute Energy: 10-7

Silicon crystal for GAMS6 from WASO4 reference material• Fabricated by PTB, Braunschweig, Germany• Characterized by INRIM, Torino, Italy

d/d < 10-8, extremely perfect silicon crystals, d known in SI units

d/d: How perfect are GAMS crystals?

L

L

k

sin4kL

Linear displacement interferometer

Angle interferometer

Angle interferometer with self-calibration

N

i

i

k

L

4arcsin2

• N Li are measured• Equation is solved for k

Result of E = mc2 test using GAMS4

Wavelength measurements are limiting

E – mc2 = -(1.2 4.3) × 10-7

S. Rainville et al., Nature 438 (2005) 1096

Accuracy reach of GAMS4

41

Stability of calibration: 2.1x10-7

Angle measurement and calibration under

atmosphere possible not better than on 10-7 level

J. Krempel, PhD LMU, 2011

spectrometer table

interferometer blockspectrometer axis

polygon + autocollimators

New instrument GAMS6

Challenge:redefinition of the

kilogram

uNm A

3

kg 10

E = mc2

kg mol

Hz

Avogadro project

Number of atoms in 1 kg

9090

2

90 )(

v4

UIRR

gmh

KJ

kg

2

A uchN

Routes to a new mass unit definition

Acknowledgements

Neutron EDM

Maurits van der GrintenRutherford Appleton Laboratory

Peter FierlingerTechnische Universität München

Short-range gravity

Hartmut AbeleAtominstitut Wien

E = mc2

Michael JentschelInstitut Laue Langevin

Material for this talk courtesy of: